Initially, configuration of a radio cellular network and elements of said network is determined manually by an operator and sent to a configuration entity. Then said configuration entity sends the determined configuration to each element of the network. It is to be noted that configuration is defined as radio parameters of controller of the network (for example emitted power, bandwidth used . . . ), and Neighbor Relations (NR) between cells of the network. Neighbor Relations are defined in the 3GPP standard 36.300 section 22.3.2a.
Manually managing neighbor relations in traditional radio cellular networks is a challenging task and becomes more difficult as new mobile technologies are being rolled out while 2G/3G cells already exist. For example, for LTE technology, task becomes challenging for operators, as in addition of defining intra LTE neighbor relations, the operator has to consider neighboring 2G, 3G, CDMA2000 cells as well.
Automatic Neighbor Relation (ANR) function as defined by the 3GPP aims to relieve the operator from the burden of manually managing neighbor relations. The ANR function is implemented in a controller of the network (a base station), and aims at automatically managing neighbor relations of each cell served by the controller. It consists for the controller on using terminals located in the cell for discovering neighbor cells.
Indeed, cells broadcast an identifying signature, named Physical Cell Identity (PCI), which terminals use to identify cells. These identifying signatures are not unique (there are 504 different PCIS in LTE), so cells broadcast an other identifying signature, named Cell Global Identifier (CGI), which can be detected and reported by terminals. Each cell has a unique CGI. However, detecting CGI is more difficult and time consuming comparing to detecting PCI, which implies restrictive use of CGIs detection. As a consequence, the controller manages a mapping between the PCI and the CGI. This enables a terminal to identify cells in measuring only the PCI.
The 3GPP standard defines several elementary steps for ANR function:                The controller instructs terminals located in the cell and connected with the controller, to perform ANR measurements in the neighborhood of the cell.        Each terminal sends a measurement report to the controller. This report contains PCIS, Tracking Area Codes (TACs), and all available operator codes (PLMN IDs) of detected neighbor cells.        If the relation PCI-CGI is unknown at the controller, then the controller instructs the terminals to report the CGIs of the detected cells.        The controller creates and exhibits a Neighbor Relation between the cell and every detected cell.        
There are many neighbor cells on many frequencies to discover. Indeed, there are many LTE frequencies, and many cells for each frequency. Furthermore, the ANR function also applies to other Radio Access Technologies and there can exist many UTRAN and/or GERAN and/or CDMA2000 frequencies. Every neighbor cell of every technology has to be discovered.
As the terminals population used for the ANR function is a scarce resource compared to the number of different neighbor cells to discover, they should be used efficiently.